The present invention pertains to a novel method and apparatus for sinking drill holes in underground rock formations while generating drill cores as rock samples.
The known methods of this type, as described in U.S. Pat. No. 4,518,050 and German Patent DE-C 37 01 914, are intended to optimize the core sample. In these methods, the main drill hole sections follow in the direction of the pilot hole sections and the core shaft section is drilled through the main drilling tool which includes a rotary drill bit corresponding to the rated diameter of the main drilling tool. Once the main drilling tool reaches the base of the core shaft section in the course of this drilling, it is stopped and a nearby core shaft section is drilled for core sampling. The length of the core shaft section is governed by the potentials of the particular tool design and can be quite considerable such as in the design disclosed in German Patent DE-U-88 10 844.
In the known methods, the core drilling unit in the outer housing of the core drilling tool is guided coaxially by a non-rotating guide device. When a core shaft section is drilled, the core tube of the core drilling unit exits coaxially from the outer housing. The outer housing of the core drilling tool thus controls the direction of the advance of the core tube.